Control circuit for brake booster vehicular hill holder system

ABSTRACT

A brake booster (10, 210, 310) connected to a control circuit (120) provides a system for the continued braking of a vehicle when the vehicle is situated on an incline and the brake pedal (92) is released by the operator. Continued brake application is accomplished by utilizing a control circuit (120) responsive to vehicular attitude, clutch pedal position, ignition status, vehicular speed, and vehicular direction. The control circuit (120) is connected to the combination of a check valve and three-way solenoid valve (100, 200, 300) connected to a movable wall brake booster (10, 210, 310). The combination valve (100) is connected to a flexible hose (110) disposed interiorily of the booster (10), the other end of the flexible hose (110) connected to the input opening (32) of a three-way poppet valve (70) located at the central hub (30) of the booster (10). When the control circuit (120) senses that the vehicle is on an incline, the clutch pedal depressed, the ignition &#34;on&#34;, the speed is zero, and the vehicle not backing up, it actuates the three-way solenoid of valve (100) which continues to supply a first fluid pressure to the front booster chamber (40) while supplying a second fluid pressure for the rear booster chamber (50) via the flexible hose (110) and poppet valve (70). The vehicle operator may release the brake pedal (92) which returns slightly toward an inactive position and which opens slightly valve (70), with the brakes remaining activated because the second fluid pressure is provided to the rear chamber (50) via the hose connection (110) and valve (70) to maintain the axially displaced position of the movable wall (24).

BACKGROUND OF THE INVENTION

The present invention relates to a vehicular hill holder system whichincludes a control circuit and a booster operable by either vacuumpressure or compressed air.

Car manufacturers are attempting to provide an economical solution for along-standing problem with manual shft vehicles: how to permit thevehicle operator to manipulate the clutch pedal, brake pedal,accelerator pedal, and shift the gear lever when the vehicle isstationary on an incline. Such inclines are common at railroad crossingsand in rural and metropolitan areas.

A solution to this problem is provided by mechanical roll-back lockdevices that effect the mechanical lockup of the brake pedal throughmechanical mechanisms connected to the brake and clutch pedals. However,such devices occupy additional cab space and require assembly andinstallation costs that are an add-on to the vehicle cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an inexpensive,practical vehicular hill holder system brake booster which utilizespresently existing equipment on manual shift vehicles. It is desirablethat such a system may be included as either optional or originalequipment on a manual shift vehicle, without requiring significantmodification of the vehicle's equipment or any significant increase incost.

The present invention comprises a vehicular hill holder system whichutilizes presently existing booster equipment. A brake boosterconstructed in accordance with the present invention is connected to acontrol circuit which provides for continued braking of a vehicle whenthe vehicle is situated on an incline and the brake pedal released bythe vehicle operator. Continued braking of the vehicle is accomplishedby a control circuit responsive to vehicular attitude, clutch position,ignition status, vehicular speed, and vehicular direction. The controlcircuit is connected to the combination of a check valve and three-waysolenoid valve connected with the casing of a moveable wall brakebooster. The check valve and three-way solenoid valve are connected to aflexible hose disposed interiorily of the casing, the other end of theflexible hose being connected to the input opening of a three-way valvelocated at the center hub of the brake booster. When the control circuitsenses that the vehicle is on an incline, the clutch depressed, theignition "on", the speed is zero, and that the vehicle is not backingup, it actuates the three-way solenoid valve which permits the continuedsupply of a first fluid pressure to the front booster chamber whilesupplying a second fluid pressure to the rear booster chamber via theflexible hose and three-way valve. The vehicle operator may release hisfoot from the brake pedal and the brakes remain activated because of thesecond fluid pressure being provided to the rear chamber to maintain theaxially displaced position of the movable wall. Alternative embodimentswhich maintain the displaced position of the movable wall include theuse of an inflatable bladder and a centrally disposed bellows.

The invention is described in detail below with reference to thedrawings which illustrate various embodiments of the invention, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of a brake booster constructed inaccordance with the present invention;

FIG. 2 is a schematic representation of the brake booster of FIG. 1 andthe control circuit connected thereto;

FIG. 3 is a cross-section view of an alternative embodiment of a brakebooster utilized in the present invention;

FIG. 4 is another embodiment of a brake booster utilized in the presentinvention and

FIGS. 5-7 illustrate control valves associated with the brake boostersof FIGS. 1, 3, and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is illustrated a servomotor or brake booster10 of the present invention. It should be clearly understood that thebrake boosters or servomotors utilized in the present invention may takemany different forms of conventional brake boosters being manufacturedtoday. Only slight modification is required in order for a booster unitto be used in the present invention, and almost any conventional vacuumor compressed air booster unit may be utilized. Thus, the brake boostervehicular hill holder provides a low-cost, inexpensively manufacturedunit because many of the present-day brake booster units may beutilized.

The booster 10 comprises a front shell 12 and a rear shell 14 which areattached together at rim portion 16. A master cylinder (not shown) wouldbe attached to the booster 10, and provide an actuating means foroperating the brakes of the vehicle when the master cylinder is actuatedby the actuating rod 18. The front and rear shells 12, 14 are attachedtogether at connection section 16 so as to trap the external bead 20 ofthe flexible diaphragm 22. Flexible diaphragm 22 is secured to movablewall 24 within the interior of the servomotor or booster unit 10.Diaphragm 22 terminates radially inwardly in an internal bead 26received within a groove 28 of the central hub 30.

Diaphragm 22 of movable wall 24 divides booster unit 10 into a frontchamber 40 and a rear chamber 50. Disposed within front chamber 40 is areturn spring 42 having one end mounted against front shell 12 and theother end engaging the central hub 30. Central hub 30 includes a firstpassage 32 which, in conventional booster uints, provides communicationbetween front chamber 40 and internal bore 60. Central hub 30 alsoincludes a body portion 34 which extends rearwardly to form the rearwardprojection 36 and bore 61. Bore 60 extends toward rearward projection36, and disposed in bore 60 is a standard poppet valve 70. Body portion34 includes a second passage 33 providing communication between rearchamber 50 and bore 60. Valve 70 comprises a conventional and well-knownpoppet valve structure utilized in many different booster embodimentsand applications. Included within valve 70 is a first valve seat 72,second valve seat 74, poppet member 76, first spring 78, second spring80, rear opening 82, filter 84, and a key 86. Extending through bore 60and operatively coupled to valve 70, is an input rod 90 operativelycoupled to the vehicle's brake pedal 92. The operation of valve 70 isconventional in performance.

Modification of booster unit 10 is provided by combination valve 100mounted to front shell 12. Combination valve 100 is mounted to the frontshell 12 purely as a matter of convenience; valve 100 may be mounted atvarious other locations within the vehicle and need not be mounteddirectly to the front shell. Combination valve 100 comprises thecombination of a check valve and three-way solenoid valve, asillustrated by the various embodiments in FIGS. 1, 3, and 4. Thesolenoid valve is connected by wires 101, 102 to the control circuitillustrated in FIG. 2 and which will be explained hereinafter. An aircleaner 105 is located at the bottom of valve 100 which has an inputconnection 104 extending through shell 12 into the interior of frontchamber 40. Located about connection 104 are spaced-apartcircumferential passages 106. Connection 104 is coupled to the end of aflexible hose or conduit 110 which is coiled within front chamber 40 andhas the other end coupled to central hub 30 to cover the outlet openingof first passage 32. Referring to FIG. 5, valve 100 comprises a coil108, spring biased armature 109, valve seats 113 and 115, and checkvalve 107 of extension 103 connected to a vacuum source. Energization ofcoil 108 effects displacement of armature 109 which closes valve seat113 and opens valve seat 115. The vacuum source continues to beconnected with the front chamber 40 by way of extension 103, check valve107 and passages 106, while connection 104 and conduit 110 are connectedwith atmosphere via air cleaner 105 and open valve seat 115.

As can be seen from the above description, a conventional brake boosterunit or servo motor may be modified for use in the present invention bymeans of a flexible connection providing communication between acombination check valve and three-way solenoid valve and the frontchamber input opening of the central hub passage communicating with thepoppet valve. Other alternative embodiments can provide the samefunctions accomplished by the above unit, and such other structures arecontemplated as being within the scope of the present invention. Examplealternative embodiments illustrating how a booster unit may be modifiedin order to operate in accordance with the present invention, areillustrated in FIGS. 3 and 4, which will be described in detail.

Referring to FIG. 2, there is illustrated a control circuit 120 utilizedwith the present invention. The vehicle's battery 124 is connected toignition switch 126 coupled by wire 127 to clutch pedal switch 128.Clutch pedal switch 128 provides an output in accordance with theposition of the clutch. If the clutch pedal is depressed or "in", suchthat the vehicle is not in gear, then clutch pedal switch 128 providesan output through line 133 connected in series with a vehicle attitudeswitch 140. However, if the clutch pedal is released such that thevehicle may be "in gear" or in neutral, then clutch pedal switch 128provides an electrical output through line 136 to the "in gear" switch150. Vehicle attitude switch 140 may comprise any type of conventionalmercury level switch or other device which will provide a switch closurewhen the vehicle is situated at a predetermined angle. Line 142 connectsattitude switch 140 with the zero speed sensor 160. Vehicle zero speedsensor 160 comprises a sensor which receives inputs indicative of thevehicle's direction of movement and whether or not the vehicle is movingor stationary. The vehicle's back-up light switch 170 provides anelectrical output through line 172 so that if the vehicle is backing up,a signal is relayed via line 172 to zero speed sensor 160 whereby anoperative output signal is not effected by the sensor 160. In otherwords, back-up light switch 170 provides a "defeat" instruction to zerospeed sensor 160. A cruise control transducer 166 normally utilized inconjunction wtih the speedometer cable of a vehicle, provides anindication of whether or not the vehicle is moving. Cruise controltransducer 166 provides a pulse output to the vehicle's cruise controldevice (not shown), and it is the pulse output which is used also as anoutput signal through line 144 to zero speed sensor 160. When anelectrical pulse output from transducer 166 is received by speed sensor160, the sensor will not provide an output for operation of thecombination valve 100. Zero speed sensor 160 is connected by line 176 totime delay switch 177 which is connected via line 101 to the valve 100.

Turning to another branch of circuit 120, the "in gear" switch 150comprises a switchin the gear housing of the vehicle, which is closedwhenever the vehicle is "in gear", whether stationary or moving. Switch150 is connected via line 178 to a zero speed switch 180 coupled bymechanical connection 182 to zero speed sensor 160. If zero speed sensor160 does not receive inputs from back-up light switch 170 and cruisecontrol transducer 166, then an output to line 176 is effected by sensor160 and also zero speed switch 180 is closed. However, if zero speedsensor 160 receives an input from either switch 170 or transducer 166,then zero speed switch 180 is open so that an electrical signal will notpass from line 178 to line 179. Zero speed switch 180 is connected byline 179 to a time delay relay 190. Time delay relay 190 is aconventional device that delays any output signal for a period ofapproximately ten seconds. Relay 190 is connected: (1) by mechanicalconnection 192 to a time delay relay switch 194 located between lineconnections 196 and 197, (2) by mechanical connection 193 to delayswitch 177, and (3) by line 198 to line 197. The ignition switch 126 isconnected buy line 196 to time delay switch 194 so that when the switch194 is closed, an output is permitted through line 197 to a warninglight 199 and to line 198 for transmission to relay 190. Warning light199 may be a standard LED or other suitable illuminant visible to thevehicle operator.

Circuit 120 operates in response to a variety of circumstances orsituations in order to determine if combination valve 100 should operateand provide continued braking of the vehicle so that the vehicleoperator may release the brake pedal without effecting release of thevehicle brakes. A vehicular brake hillholder system finds use in citiesthat are very hilly, rural areas, and at railroad track crossings whichtypically include inclines. Many vehicle operators have experienceddifficulty in keeping a manual shift vehicle from rolling backwards onan incline, because of the necessary simultaneous operation of theclutch pedal, brake pedal, shifting of the gear lever, and operation ofthe accelerator pedal when the operator is ready to accelerate thevehicle. The present invention provides a practical solution to thisproblem by providing a vehicular hill holder for manual shift vehicleswhich have brake booster units. The brake booster units may be eitherconventional vacuum brake boosters or conventional compressed air brakeboosters, both types being easily modified for use in the presentinvention.

OPERATION

The extension 103 of combination valve 100 is coupled to the engine'sintake manifold. Vacuum is provided to the valve 100 which communicatesthe vacuum via circumferential passages 106 to the front chamber 40 ofbooster 10, and via input connection 104 to conduit 110 and passage 32in central hub 30. Passage 32 communicates vacuum through second valveseat 74 to central bore 60 and through second passage 33 to rear chamber50. When the vehicle's operator depresses brake pedal 92, input rod 90is displaced such that second valve seat 74 is closed and vacuum nolonger communicated to chamber 50 via passage 32, central bore 60, andsecond passage 33. Further displacement of rod 90 opens first valve seat72 so that atmosphere may enter rear chamber 50. Atmosphere enters rearchamber 50 through rear openings 82, filter 84, bore 61, open firstvalve seat 72, bore 60, and passage 33. The introduction of atmosphericpressure into rear chamber 50 and the continued provision of vacuumwithin front chamber 40 effects a displacement of movable wall 24 whichdisplaces actuating rod 18 to operate the master cylinder (not shown)and effect braking of the vehicle. So far, operation of the brakebooster unit is in accordance with a conventional brake booster unit.Referring to FIG. 2, if the vehicle's ignition is "on" so that ignitionswitch 126 is closed, and the clutch pedal has been depressed inwardlyso that the vehicle is not "in gear", then clutch pedal switch 128provides an electrical output through line 133 to vehicle attitudeswitch 140. If the vehicle is in an inclined position, i.e., equaling orexceeding a certain predetermined angular position caused by an inclineon which the vehicle is situated, then the vehicle attitude switch isclosed and permits an electrical output through line 142 to zero speedsensor 160. As a safety feature which precludes the possibility of thevehicle being in reverse and backing up which would produce a "zerospeed" indication, back-up light switch 170 is provided with an input tosensor 160. If the vehicle is not in reverse gear for moving backwards,then no output is provided by light switch 170 through line 172 tosensor 160, and this defeat instruction is not present. Because thevehicle is stationary, no output is produced by cruise controltransducer 166 so that there is no input signal through line 144 tosensor 160. Sensor 160 permits a continual electrical output throughline 176 to time delay switch 177. Time delay switch 177 is normallyclosed and, in this situation, would permit an electrical signal to becommunicated through line 101 to combination valve 100. Upon receivingan activation signal through line 101, the three-way solenoid valve ofthe valve 100 is activated so that vacuum continues to be provided viacircumferential passages 106 to front chamber 40, but now atmosphericpressure enters through air filter 105 to connection 104, conduit 110,and first passage 32. Thus, when the vehicle operator removes his footfrom the brake pedal, brake input rod 90 is permitted to retractslightly towards its initial rest position, by means of the springs 42,78 and 80. This allows first valve seat 72 to close and valve seat 74 toopen slightly, and permit atmospheric pressure to be communicated frompassage 32 to central bore 60, passage 33, and rear chamber 50. In aconventional booster unit, at this point in operation, vacuum pressurewould have been communicated via passage 32 to central bore 60, secondpassage 33, and rear chamber 50 in order to effect the return of movablewall 24. However, in this case atmospheric pressure continues to beprovided to rear chamber 50 via passage 32, slightly open second valveseat 74, central bore 60, and second passage 33. The brakes of thevehicle remain activated, allowing the operator to remove completely hisfoot from the brake pedal. The continued supply of atmospheric pressure,or in the case of compressed air vacuum boosters, a second higher fluidpressure, to the rear chamber ensures that movable wall 24 remains inits activated position which effects continued actuation of the mastercylinder and braking of the vehicle.

Referring again to FIG. 2, when the vehicular operator decides toaccelerate the vehicle by shifting the gear lever, releasing the clutchpedal and depressing the accelerator pedal, the release of the clutchpedal opens clutch pedal switch 128 to terminate the electrical signalcommunicated through lines 133, 142, 176, and 101 to three-way solenoidvalve of combination valve 100. The opening of this portion of circuit120 permits the solenoid valve to return to its initial inactiveposition wherein vacuum is communicated again via connection 104, hose110, passage 32, slightly open second valve seat 74, and central bore 60to second passage 33 and rear chamber 50. Thus, deactivation of thethree-way solenoid valve operatively effects deactivation of the brakesas movable wall 24 returns toward its initial at-rest position. Thecessation of the supply of atmospheric pressure to rear chamber 50permits movable wall 24 to retract under the force of spring 42, towardan inactive position which results in a full return of poppet valve 70to the position illustrated in FIG. 1.

As follows from the detailed description above, the present inventionprovides a vehicular hill holder system in the form of a control circuitand a power brake booster unit that remains in an activated position inorder to provide continued braking of the vehicle, when certainpredetermined parameters are present. These parameters include theclutch pedal position, vehicular attitude, speed of the vehicle, anddirection of movement, if any, of the vehicle. When the variousparameters are present, control circuit 120 provides an electricalsignal to effect operation of combination valve 100 and operativelymaintain the displaced position of the movable wall 24 and activation ofthe brakes.

Additional safety features have been built into circuit 120 so that ifcertain situations should occur, booster unit 10 will not be activatedand brake the vehicle at an inappropriate time. It is possible that avehicle could be travelling on an incline when the speedometer cable ofthe vehicle breaks. If the speedometer cable breaks, then no inputsignal indicating motion of the vehicle would be provided to zero speedsensor 160. The zero speed sensor would then operate in the same manneras if the vehicle were stationary. Should the vehicle operator thendepress the clutch pedal while the vehicle is moving up an incline, witha broken speedometer cable, booster unit 10 could then be activated andcause a sudden braking of the vehicle. In order to prevent this fromhappening, clutch pedal switch 128, "in gear" switch 150, zero speedswitch 180, and time delay relay 190 are provided. In theabove-described situation where the vehicle is travelling up an inclinewhen the speedometer cable breaks, if the clutch pedal is releasedoutwardly, then clutch pedal switch 128 permits an electrical signal topass through line 136 to the "in gear" switch 150. If the vehicle is "ingear", then switch 150 is closed and permits the signal to pass throughline 178 and closed zero speed switch 180. Zero speed switch 180 isclosed because the speedometer cable is broken and sensor 160 does notoperate responsively thereto. Closed zero speed switch 180 permits thesignal to pass through line 179 to time delay relay 190. Time delayrelay 190 delays operation of its switch contacts and the actuation ofmechanical connections 192 and 193 for a period of approximately tenseconds. Once ten seconds have elapsed, mechanical connections 192 and193 are actuated so that normally closed time delay switch 177 is openedand normally open time delay switch 194 is closed. Thus, should thevehicle operator decide to shift gears and depress the clutch pedalinwardly, an electrical output through line 133, vehicle attitude switch140, line 142, zero speed sensor 160 and line 176 would not reachcombination valve 100 and cause operation thereof. Likewise, time delayswitch 194 is closed so that the warning light 199 is activated and thevehicle operator made aware of a failure in the circuit, and a signalprovided through line 198 to keep relay 190 energized and switch 177open.

If the vehicle is parked and the operator has turned on the ignitionswitch, depressed the clutch, and is utilizing the hill holder,operation of the hill holder will be permitted for an unlimited periodof time or until the vehicle operator releases the clutch pedal in orderto place the vehicle in gear. Here the hill holder system is operatingat a stationary position of the vehicle when the speedometer cable isbroken, whereby the vehicle operator may use the hill holder system foran unlimited period of time or until the clutch pedal is released toplace the vehicle in gear. At that time, an electrical signal would passfrom the now closed "in gear" switch 150 via line 178 through the zerospeed switch 180 and line 179 to time delay relay 190. After a timedelay period of approximately ten seconds, the contacts of mechanicallyconnected switches 194 and 177 would transfer. Switch 177 would open torender the hill holder system inoperative. Switch 194 has a dualfunction wherein (1) a signal from line 196 passes along line 197 toenergize warning light 199, and (2) a signal passes along line 198 toprovide a latching signal to time delay relay 190. The latching signalprovided to relay 190 will hold relay 190 energized, provided the tensecond delay has occurred, until the ignition switch 126 is turned off.Turning off ignition switch 126 will reset the system to the normaloperative ready state.

FIG. 3 illustrates an alternative brake booster embodiment having aninflatable bladder 208. A valve 200 (three-way solenoid valve) isoperatively connected to the neck 202 of bladder 208 disposed withinrear chamber 250 of the booster unit 210. Valve 200 provides vacuum tobladder 208 and comprises a mechanism distinct from check valve 204, theuse of separate valves 200, 204 also being applicable to the embodimentsof FIGS. 1 and 4. Referring to FIG. 6, valve 200 comprises a coil 207,spring biased armature 209, valve seats 213 and 215, and extensions 203and 206. Energization of coil 207 effects displacement of armature 209which closes valve seat 213 and opens valve seat 215. Closed valve seat213 terminates the extension 206 connection with a source of vacuumthrough extension 203, and open valve seat 215 connects extension 206with atmosphere through air cleaner 205. Booseter unit 210 comprises aconventional vacuum booster unit or a booster unit utilizing compressedair. The front chamber 240 of unit 210 is provided continuously withvacuum via check valve 204 connected to the intake manifold, vacuumbeing communicated through first passage 232, second valve seat 274,central bore 260, and second passage 233 to rear chamber 250. Lateraldisplacement of the input rod 290 effects operation of poppet valve 270in the conventional manner such that second valve seat 274 is closed toprevent vacuum from being communicated to rear chamber 250 and firstvalve seat 272 opens to permit atmosphere to enter central bore 260,second passage 233, and rear chamber 250. Movable wall 224 is displacedto effect actuation of a master cylinder (not shown) through theactuating rod 218. The circuit 120 described above would be used inconjunction with the embodiment of FIG. 3, and would be connected to thecombination valve 200. If the vehicle is on an incline, stationary, notbacking up, with the brake pedal and clutch pedal depressed, a signalwould be provided via line 201 to actuate the three-way solenoid valvecontained in valve 200 and permit atmosphere to be communicated throughconnection 206 and neck 202 to bladder 208. Atmospheric pressure wouldinflate bladder 208 so that it is fully inflated between movable wall224 and rear shell 214. Thus, when the vehicle operator removes his footfrom the brake pedal, even though valve seat 272 closes and valve seat274 opens slightly, bladder 208 remains inflated and maintains thedisplaced position of movable wall 224 to continue braking of thevehicle. Upon release of the clutch pedal by the vehicle operator,control circuit 120 would deactivate valve 200 which again suppliesvacuum to bladder 208 to deflate it and allow movable wall 224 to returnto an inactive position.

Referring to FIG. 4, a third embodiment of the brake booster unit isillustrated. A booster unit 310 includes a flexible bellows 410 at thecentral area thereof, one end 411 of the bellows being connected to thefront shell 312 and the other end 412 connected to movable wall 324.Check valve connection 304 enables vacuum to be continuouslycommunicated to front chamber 340, and connection 306 provides forcommunication of vacuum to the interior of bellows 410. The valve 300(three-way solenoid valve) is coupled to previously described controlcircuit 120 so that when the control circuit operates in accordance withthe above-described conditions, an electrical signal to combinationvalve 300 effects operation of the three-way solenoid valve containedtherein. Operation of valve 300 terminates the communication of vacuumvia connection 306 to the interior of bellows 410 and permits atmosphereto be communicated through connection 306, bellows 410, first passage323, slightly open second valve seat 374, and interior bore 360 tosecond passage 333 and rear chamber 350. Referring to FIG. 7, valve 300comprises an extension 303, coil 308, spring biased armature 309, valveseats 313 and openings 305 and 307. Opening 307 extends laterally fromthe central opening of armature 309 and can be aligned with opening 305that includes an air cleaner. Energization of coil 308 displacesarmature 309 which closes valve seat 313 and aligns hole 307 with hole305 to permit atmosphere to be communicated through seat 313 toconnection 306. A vacuum source connected with extension 303 continuesto communicate with check valve 304. Thus, booster unit 310 operates inthe same manner as the booster unit illustrated in FIG. 1, although unit310 utilizes a bellows 410 to provide an alternative means forcommunicating vacuum or atmosphere to first passage 332 and poppet valve370.

Although this invention has been described in connection with theillustrated embodiments, it will be obvious to those skilled in the artthat various changes may be made in the form, structure, and arrangementof the parts without departing from the invention.

We claim:
 1. A braking assistance servo motor system operable tomaintain the braking of a vehicle when the brake pedal is releasedtoward an inactive braking position, comprising a brake booster having afirst chamber, a working chamber, first valve means responsive to thebrake pedal, output means for operatively actuating brakes of thevehicle, and second valve means operatively connected with the booster,and control circuit means for sensing vehicular parameters andoperatively connected to said second valve means, said brake boosteroperating responsively to said brake pedal by utilizing a pressuredifferential between the chambers to displace the output means andactuate the brakes, the control circuit means sensing the parameters ofvehicular attitude, clutch position, and vehicular speed to actuateresponsively thereto the second valve means and provide fluid pressureto said brake booster and maintain the displacement of the output meansand actuation of the brakes after the brake pedal has been released,said control circuit means including a clutch pedal position mechanism,transmission gear switch, a second switch responsive to vehicle speedsensor means, a time-delay relay, third and fourth switches responsiveto the time-delay relay, and a connection between the fourth switch andtime-delay relay, the control circuit means rendering inoperative thesecond valve means when the vehicle speed sensor means is inoperative byeffecting a signal through the clutch pedal position mechanism,transmission gear switch, second switch which is actuated by a lack ofsignaling from the speed sensor means, and time-delay relay which isactuated by the signal and operates the third switch to preventactuation of the second valve means and fourth switch to permitcontinued energization of said time-delay relay through the connection.2. The system in accordance with claim 1, further comprising aninflatable device disposed in the working chamber and in communicationwith said second valve means, said inflatable device receiving the fluidpressure to be inflated thereby and operatively maintain displacement ofthe output means.
 3. The system in accordance with claim 1, furthercomprising communication means for connecting said second valve meanswith said first valve means, said communication means receiving saidfluid pressure and transmitting the fluid pressure to the first valvemeans for communication with the working chamber.
 4. The system inaccordance with claim 3, wherein the communication means comprises aflexible conduit disposed interiorly of the booster.
 5. The system inaccordance with claim 3, wherein the communication means comprises abellows disposed within said booster.
 6. The system in accordance withclaim 1, wherein said second valve means continuously provides lowerfluid pressure to said first chamber.
 7. The system in accordance withclaim 1, wherein the clutch pedal position mechanism permitstransmission of said signal when an associated clutch pedal is in areleased position.
 8. The system in accordance with claim 7, wherein asubsequent depression of the clutch pedal prevents transmission of saidsignal through the clutch pedal position mechanism and the fourth switchcontinues to permit energization of the timedelay relay through theconnection which comprises an electrical connection.
 9. The system inaccordance with claim 7, wherein the transmission gear switch permitstransmission of said signal when an associated vehicle transmission isactivated and effecting movement of the vehicle.
 10. The system inaccordance with claim 1, wherein the operation of the fourth switch alsoeffects operation of a warning device.
 11. The system in accordance withclaim 10, wherein the warning device comprises a light-emitting diodedevice.
 12. The system in accordance with claim 10, wherein the fourthswitch is connected to a vehicle ignition switch and transmits a signalto the warning device when the fourth switch is closed by saidtime-delay relay.
 13. A braking assistance servo motor system operableto maintain the braking of a vehicle when the brake pedal is releasedtoward an inactive braking position, comprising a casing, an assistancepiston assembly displaceable in the casing and dividing the casing intotwo chambers, an output member actuable by the piston assembly, an inputmember, first valve means operatively coupled with said casing and incommunication with said chambers, second valve means for controllingfluid pressure flow, means for connecting said second valve means andfirst valve means, and control means for sensing vehicular parametersand operatively connected to said second valve means, said second valvemeans providing a first fluid pressure to the second one of saidchambers via the connection means and first valve means, actuation ofthe input member effecting actuation of said first valve means toterminate the provision of said first fluid pressure to said secondchamber and admit a second fluid pressure to said second chamber andthereby cause displacement of said assistance piston assembly, thecontrol means sensing the parameters of vehicular attitude, clutchposition, and vehicular speed to actuate responsively thereto the secondvalve means which provides said second fluid pressure to said secondchamber via the connection means and first valve means and allowdeactuation of said first valve means, said control means including aclutch pedal position mechanism, transmission gear switch, a secondswitch responsive to vehicle speed sensor means, a time-delay relay,third and fourth switches responsive to the time-delay relay, and aconnection between the fourth switch and time-delay relay, the controlmeans rendering inoperative the second valve means when the vehiclespeed sensor means is inoperative by effecting a signal through theclutch pedal position mechanism, transmission gear switch, second switchwhich is actuated by a lack of signaling from the speed sensor means,and time-delay relay which is actuated by the signal and operates thethird switch to prevent actuation of the second valve means and fourthswitch to permit continued energization of said time-delay relay throughthe connection.
 14. A brake booster-assisted braking system operable onan incline to maintain braking of a vehicle with the brake pedalreleased by the vehicle operator, comprising a casing having a valvedisposed adjacent one end wall of the casing and actuated by anoperatively connected brake pedal, actuating rod means engaging thevalve means and extending through the other end wall of the casing tooperatively engage brake actuator means, a movable wall disposed in thecasing to divide the casing into a fist chamber and a second chamber andacting on said actuating rod means, control valve means forcommunicating fluid pressures to the interior of said casing, connectionmeans for connecting said control valve means with said valve, andcontrol circuit means for sensing vehicular parameters and connected tosaid control valve means, displacement of the operatively connectedbrake pedal actuating said valve to terminate the communication of afirst fluid pressure from said control valve means to said secondchamber via the connection means and valve and providing a second fluidpressure to said second chamber to effect a pressure differentialbetween said chambers which causes displacement of said movable wall andactuating rod means to operate the brake actuator means and effectbraking of the vehicle, the control circuit means sensing the parametersof vehicular attitude, clutch position, and vehicular speed andresponsively thereto actuating the control valve means so that saidsecond fluid pressure is provided by the control valve means to thesecond chamber via the connection means and valve to maintain thebraking of the vehicle upon release of the brake pedal which deactivatesthe valve, said control circuit means including a clutch pedal positionmechanism, transmission gear switch, a second switch responsive tovehicle speed sensor means, a time-delay relay, third and fourthswitches responsive to the time-delay relay, and a connection betweenthe fourth switch and time-delay relay, the control circuit meansrendering inoperative the control valve means when the vehicle speedsensor means is inoperative by effecting a signal through the clutchpedal position mechanism, transmission gear switch, second switch whichis actuated by a lack of signaling from the sensor means, and time-delayrelay which is actuated by the signal and operates the third switch toprevent actuation of the control valve means and fourth switch which isactuated and permits continued energization of said time-delay relaythrough the connection.
 15. The brake booster-assisted braking systemaccording to claim 14, wherein said control circuit means senses theparameters of vehicular attitude, clutch position, ignition status,vehicular speed, and vehicular direction.
 16. The brake booster-assistedbraking system according to claim 15, wherein said control valve meanscomprises the combination of a check valve and a three-way solenoidvalve operating responsively to signals from said control circuit means,so that operation of the three-way solenoid valve effects a continuedsupply of the first fluid pressure to said first chamber and the supplyof said second fluid pressure to the second chamber via the connectionmeans and valve.
 17. The brake booster-assisted braking system accordingto claim 15, wherein the connection means comprises a flexible tubehaving one end connected to said control valve means and the other endconnected to said valve.
 18. The brake booster-assisted braking systemaccording to claim 16, wherein the connection means is disposedinteriorly of said casing.
 19. The brake booster-assisted braking systemaccording to claim 15, wherein the brake booster comprises a vacuumbrake booster with the first fluid pressure providing vacuum and thesecond fluid pressure comprising atmospheric pressure.
 20. The brakebooster-assisted braking system according to claim 14, wherein saidcontrol valve means continuously supplies said first pressure to thefirst chamber.
 21. The brake booster-assisted braking system accordingto claim 15, wherein the control circuit means includes a connectionwith a back-up light switch.
 22. A vehicle brake booster systemutilizing a pressure differential to effect braking of the vehicle,comprising: a casing having a valve actuated by an operatively connectedbrake pedal, master cylinder actuating means connected with the valve,at least one interior movable wall dividing the casing into a frontchamber and a rear working chamber and acting on said actuating means,an inflatable device disposed in said rear working chamber forengagement with said interior movable wall, control valve means forcommunicating with said inflatable device, and control circuit means forsensing vehicular parameters and operatively connected to said controlvalve means, displacement of the brake pedal actuating said valve toterminate the provision of a first fluid pressure to the rear workingchamber and provide through said valve a second fluid pressure to saidrear working chamber in order to displace said movable wall, and saidcontrol circuit means selectively actuating said control valve meanswhich effects the supply of said second fluid pressure to said device toeffect inflation thereof such that the device expands against saidmovable wall and maintains the displaced position of the wall when saidbrake pedal is released and deactuates said valve, said control circuitmeans including a clutch pedal position mechanism, transmission gearswitch, a second switch responsive to vehicle speed sensor means, atime-delay relay, third and fourth switches responsive to the time-delayrelay, and a connection between the fourth switch and time-delay relay,the control circuit means rendering inoperative the control valve meanswhen the vehicle speed sensor means is inoperative by effecting a signalthrough the clutch pedal position mechanism, transmission gear switch,second switch which is actuated by a lack of signaling from the sensormeans, and time-delay relay which is actuated by the signal and operatesthe third switch to prevent actuation of the control valve means andfourth switch to permit continued energization of said time-delay relaythrough the connection.
 23. The vehicle brake booster system inaccordance with claim 22, wherein said inflatable device has an outletextending through an opening in the casing of the booster, the outletconnected to said control valve means.
 24. The vehicle brake boostersystem in accordance with claim 22, wherein said inflatable devicecomprises an inflatable bladder disposed in the rear working chamberbetween the movable wall and the casing, the bladder receiving saidfirst fluid pressure from said control valve means prior to actuation ofsaid control valve means by said control circuit means.
 25. A processfor maintaining actuation of a vehicular braking assistance servo motorwhen the vehicle is situated on an incline, comprising the steps of: (a)coupling first valve means with a casing of a servo motor and inoperative connection with an input member, an output member, and anassistance piston assembly dividing the casing into chambers, (b)locating second valve means for communiation with a first chamber ofsaid chambers, (c) connecting means for communication to said secondvalve means and said first valve means, (d) coupling control circuitmeans with said second valve means, the control circuit means operatingresponsively to the parameters of vehicular attitude, clutch position,transmission gear engagement, and vehicular speed, (e) supplying a firstfluid pressure to said second valve means for joint communication of thefirst fluid pressure to said first chamber and to a second chamber ofsaid chambers, the second chamber receiving said first fluid pressurevia the communiation means and first valve means, (f) displacing saidinput member to actuate said first valve means which terminates thesupply of said first fluid pressure to the second chamber and provides asecond fluid pressure to the second chamber, and thereby effectingdisplacement of said assistance piston assembly and output member, (h)maintaining the displaced position of said assistance piston assemblywhen said vehicle is stationary on an incline, by actuating the secondvalve means responsively to said control circuit means in order toprovide a continuous supply of said second fluid pressure through saidcommunication means and first valve means to the second chamber upondeactuation of said first valve means, and (i) preventing actuation ofthe second valve means when speed sensor means of said control circuitmeans is inoperative, the control circuit means responding to theparameters of clutch position, transmission gear engagement and theinoperativeness of said speed sensor means to operate a time-delay relaywhich prevents a signal from activating said second valve means, thecontrol circuit means including a connection providing continuedenergization of the time-delay relay after operation thereof.
 26. Theprocess in accordance with claim 25, further comprising the step ofdisposing said communiation means interiorly of said casing.
 27. Theprocess in accordance with claim 25, further comprising the step ofceasing maintenance of said displaced position of the piston assembly bydeactuating the second valve means responsively to the parameters ofvehicular attitude, clutch position, and vehicular speed as sensed bysaid control circuit means.
 28. A process for maintaining actuation of avehicular braking assistance servo motor when the vehicle is situated onan incline, comprising the steps of: (a) coupling first valve means witha casing of a servomotor and in operative connection with an inputmember, an output member, and an assistance piston assembly dividing thecasing into chambers, (b) locating second valve means for communiationwith said servo motor, (c) coupling control circuit means with saidsecond valve means, the control circuit means operating responsively tothe parameters of vehicular attitude, clutch position, transmission gearengagement, and vehicular speed, (d) displacing said input member toactuate said first valve means which effects displacement of saidassistance piston assembly and output member by means of a pressuredifferential between the chambers, (e) maintaining the displacedposition of said assistance piston assembly when said vehicle isstationary on an incline and the first valve means deactuated, byactuating the second valve means responsively to said control circuitmeans in order to provide a fluid pressure to said servo motor tomaintain actuation thereof, and (f) preventing actuation of the secondvalve means when speed sensor means of said control circuit means isinoperative, the control circuit means responding to the parameters ofclutch position, transmission gear engagement and the inoperativeness ofsaid speed sensor means tooperate a time-delay relay which prevents asignal from activating said second valve means, the control circuitmeans including a connection providing continued energization of thetime-delay relay after operation thereof.
 29. The process in accordancewith claim 28, further comprising the step of supplying said fluidpressure through said second valve means to inflate bladder means in achamber of said casing.
 30. The process in accordance with claim 28,further comprising the step of disposing interiorly of the casingcommunication means for transmitting fluid pressure from the secondvalve means to the first valve means.
 31. The process in accordance withclaim 28, further comprising the step of the second valve meanssupplying lower fluid pressure to one of said chambers.